The directional effect of differential multi-microphone systems depends decisively on how well the particular microphones used are matched with regard to amplitude and phase response. Only when the incoming microphone signals are amplified and delayed equally relative to frequency can the subsequent differential forming of the microphone signals generate a precise cancellation in one or more directions (spatial notches).
As a solution for equalizing amplitude frequency responses, it is known to match the amplitudes of the microphones used to one of the microphones, designated as the reference microphone. The amplification factors required to match/adjust the microphones are calculated by quotient formation of the time-averaged amplitudes of the microphone signals and of the reference microphone signals.